This invention relates to a double-cylinder pump especially for the conveying of cement from an input feed container with two openings each leading to a respective one of two conveying cylinders, in front of which openings one end of a driven distribution pipe is pivotable, said one end being sealed with the aid of a fixed spectacles-shaped plate and an axially arranged, preferably adjustable, wearing ring.
With pumps of this kind which are used generally for the conveying of viscous porridge-like masses, in practice mainly cement, the cement which is to be conveyed flows into one conveyor cylinder from the input feed container whilst the other conveyor cylinder which has been filled by the previous stroke, delivers its contents through the distribution pipe into a conveyor conduit connected to the input feed container.
The drive serves for delivering the necessary movement energy for the swivelling movement of the distribution pipe corresponding to the respective strokes of the pump. The end of the distribution pipe nearer to the conveyor cylinder must be sealed so that on pressure strokes of the conveyor cylinder, leakage, particularly of liquid and fine grained components of the conveyed medium, between the cylinder opening and the distribution pipe is prevented. With the conveying of cement, there exists the danger that such leakage could cause weakening of the cement mix. On the one hand, the seal must withstand the pressures which result from the considerable conveying heights over which modern cement pumps must operate. On the other hand the seal must permit the assimilation of the wear which occurs between the movable and fixed parts of the seal.
It is known to install the wearing ring in a spectacles-shaped plate (i.e. a plate containing two apertures side by side) for each conveyor cylinder opening, and to install the shaft of the distribution pipe drive so that it can be adjusted axially, thereby allowing the end of the distribution pipe on the side of the conveyor cylinder to be displaced to assimilate the wear between the wearing ring and the openings of the spectacles-shaped plate in the preliminary feed container U.S. Pat. No. 3,726,614. Whilst, in this known device, the shaft of the distribution pipe drive can be adjusted with a screwed-on nut, there can, with a further, also previously known, device of this kind, also be provided an additional pressure screw which acts between the distribution pipe and a swivel lever connected to the shaft (German Offenlegungsschrift No. 2362670).
It is furthermore known, to mount the wearing ring so that it is slightly displaceable axially on the end of the distribution pipe nearer to the conveyor cylinder and to leave a groove between the end of the distribution pipe and the ring, in which groove the hydrostatic pressure of the conveyed medium acts on the one face, on one side of the ring, and on the other face on, the end side of the distribution pipe. By this, the distribution ring should be automatically pressed on to the spectacles-shaped plate, and thus be adjusted in accordance with the wear with the aid of the hydrostatic pressure. (Zeitschrift Baumaschinendienst, issue May 5, 1976, page 234).
Practical experience with seals of this kind shows that cement pumps thus installed do not function satisfactorily. On the one hand, the wear is uneven in so far as the path lengths traversed by the different paths during swivelling of the distribution pipe differ appreciably from each other. For this reason, increased wear occurs with increases in the distance from the pivot shaft. This uneven wear occurs after a relatively short time of operation because the distance between the pivot axis and the cylinder openings is kept as small as possible. The wear can however not be completely assimilated by axial adjustment of the wearing ring. Apart from this, the distributor pipe is pivoted out of the plane of the spectacles-shaped plate by the hydrostatic pressure of the conveyor medium because of the elastic deformation of the body of the pipe, and/or because of the necessary play in the mounting of the distribution pipe. In this manner a gap occurs which is largest in the areas furthest, removed from the pivoting shaft of the drive. If however the task of pressing the wearing ring is left to the hydrostatic pressure alone, then the wearing ring can, when operating against a low conveying resistance, be moved away from the spectacles-shaped plate by the entry of sand or foreign bodies between the two elements, which effect can lead to jamming of the distribution pipe.
The essential task of the invention is to form the seal at the end of the distribution pipe nearer to the conveyor cylinder in such a manner that deterioration of the seal owing to the influence of distortion and displacement because of the hydrostatic pressure can not occur. In a preferred embodiment of the invention uneven wear can be compensated in a pump which has a relatively short distance between the pivot shaft and the cylinder openings.
According to the invention this task is resolved in that the wearing ring is located on a clamping or pressing device and the pipe end and the wearing ring are arranged to be movable with respect to each other and sealed off against each other.
Thus the invention provides a double-cylinder pump, comprising an input container with two openings, two conveyor cylinders each in communication with a respective one of said openings, a driven distribution pipe with one end pivotally movable between the two openings which end is sealed with the aid of a fixed spectacles-shaped plate surrounding said openings an axially arranged wearing ring for sealing said pipe end to the spectacles-shaped plate and a clamping device on which the wearing ring is positioned, the end of the distribution pipe and the wearing ring being arranged to be movable with respect to each other and sealed off one against the other.
For preference, the clamping device is coupled to a drive for the pivotal movement of the distribution pipe and furthermore the wearing ring for its part is located so that it can be pivoted.
In that the wearing ring is connected to a clamping device not influenced by the distribution pipe, and that the end of the distribution pipe nearer to the conveyor cylinder is sealed so as to be movable relative to the wearing ring, the condition is created that unavoidable movements of the distribution pipe and the action of the conveying pressure have no unfavourable influence on the tightness of the metallic seal between cylinder openings and the wearing ring. On the other hand, the movable locating of the end of the distribution pipe in the wearing ring permits pivotal movement of the wearing ring with respect to the end of the pipe which, for its part, permits the seating of the wearing ring on the spectacles-shaped plate, even after uneven wear, for example by the known axial displacement, of the pivot shaft. Under these conditions, the wearing ring engages with the spectacles-shaped plate over its entire periphery because the wearing ring correspondingly pivots and, by this, makes possible an overall assimilation of varying wear. The sealing of the end of the pipe to wearing ring does not present a problem. The advantages which can be achieved by the invention lie principally in that, with considerable conveying heights, and correspondingly high pressures, absolutely tight connections of the distribution pipe to the cylinder openings can be attained and that if need be, by using known auxiliary arrangements, the varying wear can be compensated and the appearance of additional spaces in the sealing, which can lead to lack of tightness, can be prevented.
Preferably, pivot pins are used for the pivotable positioning of the wearing ring through which pivot pins runs the pivot axis of the wearing ring. According to an embodiment of the invention the pivot pins are located directly on a lever, which forms part of the distributor pipe drive. In another embodiment of the invention bearings are used which consist of convex and concave segments.
In a further embodiment of the invention a frame is provided which is adjustably mounted with respect to the spectacles-shaped plate, and which serves for the guiding of the moving part of the seal. The end of the pipe can be movably positioned and sealed in the wearing ring and/or a guide ring can be connected to the wearing ring. Other embodiments of the invention provide for the positioning and sealing of the wearing ring in the end of the pipe.